The present invention relates to a device for controlling the thrust of an aircraft, this thrust being generated by a number of engines.
More specifically, the present invention applies to an aircraft, especially a civil transport airplane, that has a number of engines set out more or less in a line which is orthogonal to the longitudinal axis of the aircraft, and are arranged respectively so that they are symmetric with respect to said longitudinal axis.
For such an aircraft, there is generally defined a minimum specified speed that corresponds to the minimum speed for which it is possible to control the lateral behavior of the aircraft in the event of asymmetry in the thrust as a result of the failure of an engine. This minimum specified speed is characterized by the fact that when an outer engine has failed, maximum rudder has been applied, and the engines that are working are at full thrust, the heading can be maintained with less than 5.degree. of bank.
A multi-engine aircraft of this kind therefore, when on an approach flight path, with all its engines operating, needs to have a speed that is higher than said minimum specified speed so that should one of its engines fail, the other engines can be run at full thrust (over-shoot) while maintaining an angle of bank of less than 5.degree.. Of course, for the application of rudder to have sufficient effect, the speed needs to be high enough.
Said minimum specified speed therefore leads to a substantial and disadvantageous limitation to the flight envelope of the aircraft.
Furthermore, it is known that an aircraft needs to comply with a number of stipulated constraints directly associated with the thrust available and therefore indirectly associated with said minimum specified speed.
On the one hand, when during landing, an aircraft needs to overshoot for some reason or another, the thrust available needs to allow it to comply with the strict stipulated constraints regarding the climb angle. This angle in effect needs to be higher than a predetermined value which differs depending on whether or not one of the engines has failed. If the aircraft is not capable of complying with these constraints, the only possible solution is to reduce the maximum permissible mass for landing.
On the other hand, another stipulated constraint requires the aircraft to be able to set down on the takeoff and landing runway 15 minutes after having taken off from there. For this, its mass must not exceed a maximum specified mass for landing, which mass is directly associated with the thrust available. To satisfy this condition, either said aircraft needs to be equipped with a system for dumping its fuel, or its mass on take-off needs to be limited. Of course neither of these solutions is satisfactory, especially as regards the optimization of aircraft performance.